1. Field of the Invention
This invention relates to an image (or picture) processing method for processing a grayscale image (or picture), by which grayscale images of color or monochrome photographs, characters and so on are processed by being converted into digital signals.
Further the present invention relates to an image processing method by which the data amount of image signals are compressed.
Still further the present invention relates to a method for restoring grayscale image from compressed signal data.
2. Description of the Related Art
Hitherto, according to such a kind of a conventional image processing method for processing a grayscale image, an image is divided into fine (or minute) pixels (or pels). Then, a signal representing the density (or gray level) of an image of each of the pixels is converted into a multi-value (or multi-valued) digital signal representing multi-value data. Further, in accordance with such a conventional image processing system, the storage (or save), transfer and reproduction of the converted data (namely, the data obtained by the conversion) are performed without changing the data format thereof.
In accordance with the conventional image processing system for processing grayscale image, an image signal converted correspondingly to each pixel as a multi-value signal representing multi-value data has been processed without changing the data format thereof. Thus, in the case of employing the conventional image processing system, massive amounts of data should be processed. Consequently, the conventional image processing method has drawbacks in that a mass storage device (or a large scale memory device) is necessary to store a great quantity of data and that extremely long time is required when image signals are transferred by, for example, data communication.
Moreover, the conventional image processing method has poor ability to process an image at the time of reproduction thereof. In accordance with the conventional image processing method, when enlarging an image, an operation of filling surplus space with fillers (namely, pad (or padding) data) is performed. In contrast, when shrinking (or condensing) the image, an operation of thinning out pixels is performed. This results not only in degradation in the picture quality but also in great difficulty in scaling (namely, enlargement/shrinkage) of the image at (or by) an arbitrary scaling factor (for example 1.5 times).
Furthermore, the image density of an image is determined by the number of pixels and thus cannot be freely changed. Thus, in the case of employing the conventional image processing method, only a signal generated correspondingly to each pixel in the same way can be inputted to a reproducing device, which is required to reproduce a high quality image, and another reproducing device adapted to simply and easily reproduce an image with low picture quality. Consequently, the conventional image processing method is extremely insufficient. Further, the picture quality of the reproduced image is not higher than the picture quality preset correspondingly to each pixel. Therefore, for instance, when using a reproducing device adapted to be able to reproduce a high quality image for printing, no high quality reproduced images, which should be obtained by such a reproducing device, cannot be obtained.
Accordingly, an object of this invention is to provide an image processing method for processing a grayscale image, by which the drawbacks of such a conventional image processing method can be eliminated and the compression of data can be easily achieved and the reproduction of a high quality image of highly processability and adaptability to the reproduction condition can be attained at the time of image reproduction by using an image reproducing device having various resolutions.
Further the present invention provide an image processing method in which only the signals of the pixels at the positions where the degree of the density variation of the grayscale images sharply change are extracted and data at the intermediate position is cut off.
To achieve the foregoing object, in accordance with the present invention, there is provided an image processing method for processing a grayscale image, which comprises the steps of: dividing a grayscale image into fine pixels and then receiving input image signals obtained by converting the densities of the pixels into multi-value digital signals, respectively; regarding pixels, at each of which the degree of variation in density abruptly changes, as characterizing the image, and selecting signals corresponding to such pixels from the image signals and taking out (or extracting) the selected signals to thereby compress a quantity of data; restoring the pixels at the time of reproduction of the image by changing the densities of pixels between each pair of adjoining two of the selected points (or pixels) uniformly (or at an average rate); and outputting signals respectively representing the restored pixels.
Further the device according to the present invention has means for extracting a relation of x-D by setting y constant, comparison means for comparing the change in variation degree of the density (D) with a predefined threshold means for representing by a vector an average relation between x and D in each of a sequence of intervals in which the change in the degree is less than the predefined threshold.
Further the image processing method according to the present invention comprises the steps of dividing a grayscale image on an x-y plane into fine pixels and then receiving input image signals obtained by converting densities of said pixels into multi-value digital signals, respectively;
extracting a relation between an x-coordinate and a density by setting a y-coordinate as being constant;
comparing a change in a degree of variation in a density for x-coordinates with a predefined threshold;
obtaining and representing an average relation between the x-coordinate and the density (D) in each of a sequence of intervals, in which the change in the degree is less than the predefined threshold, by a vector; and
outputting a vector represented signal.
Still further according to the present invention, the compressed data signal retaining only the signal of pixels at the positions where the degree of density variation in the grayscale images abruptly changes is inputted, the densities of adjacent two of the pixels in the compressed data signal are extracted, and the image signals representing pixels are restored by providing densities which change at an average rate in the range between each pair of adjoining two of the pixels to pixels in the range therebetween to restore signals.
FIG. 1 illustrates an apparatus for performing the aforementioned image processing method of the present invention. This apparatus comprises: image signal input means for inputting image signal respectively corresponding to pixels; data compression means for performing data compression by selecting and taking out only image signals respectively representing pixels, at each of which the degree of variation in density abruptly changes, from the inputted signals; image restoring means for changing the densities of pixels between each pair of adjoining two of the selected pixels at an average rate; and restored-signal outputting means for outputting signals respectively representing the restored pixels.
FIG. 1 also shows the image restoring apparatus comprising means for inputting compressed data signal retaining only the signals of pixels at the positions where the degree of variation of densities abruptly changes, means for extracting the densities at the adjacent two points in the compressed data signals, and means for restoring signals and representing the pixels, and means for outputting the restored signals.
Thus, in the case of the image processing method of the present invention, only image signals respectively representing pixels at places, at each of which the degree of variation in density abruptly changes, are selected from and taken out of multi-value image signals respectively representing pixels. Thus, signals respectively corresponding to pixels in each portion, in which the density changes uniformly, are discarded. Consequently, the quantity of data to be used is reduced (accordingly, such data is compressed). Further, when restoring a grayscale image, pixels positioned between two points (or pixels) respectively located at each pair of adjacent two of selected places are restored by setting the density of each of the pixels positioned therebetween in such a manner as to change at an average rate. Thus, the grayscale image is restored.
Further according to the present invention, the x-D relation is represented by a vector for a unit area of x-D plane, and the degree of variation of the density (D) is represented by a vector in a sequence of intervals in which the change in the degree is less than a predefined threshold, and the signal represented by the vector is outputted.
Further according to the present invention, the pixels between two adjacent points in the compressed data are restored by giving a density signal which changes in average.